The invention relates generally to disease resistance genes from plants and more particularly to anthracnose resistance genes from legumes.
Plants can be damaged by a wide variety of pathogenic organisms including viruses, bacteria, fungi and nematodes. Annual crop losses due to these pathogens is in the billions of dollars. Synthetic pesticides are one form of defense against pathogens and each year thousands of tons of such chemicals are applied to crops. However, there are concerns regarding the short term and long term environmental damage due to chemical pesticides use, as well as inherent risks to human health.
Plants also contain their own innate mechanisms of defense against pathogenic organisms. Natural variation for resistance to plant pathogens has been identified by plant breeders and pathologists and bred into many crop plants. These natural disease resistance genes often provide high levels of resistance to pathogens and represent the most economical and environmentally friendly form of crop protection.
Genetic resistance is the most efficient way to control anthracnose, the disease caused by the fungus Colletotrichum lindemuthianum, in common bean (Phaseolus vulgaris L.). The high genetic variability observed in the pathogen population (Balardin, R. S. et al., Phytopathology 87:1184-1191 (1997)) is associated with different resistance genes present in the host (Balardin, R. S. et al., J. Amer. Sco. Hort. Sci. 123(6):1038-1047 (1998)). Seven independent dominant disease resistance genes (Co-1 to Co-7) controlling anthracnose in bean have been described (Balardin, R. S. et al., Phytopathology 87:1184-1191 (1997)). Each of these genes confers resistance to certain races of the pathogen strongly suggesting that resistance to anthracnose in common bean follows the gene-for-gene theory (Flor, H. H., Phytopathology 45:680-685 (1947)). Certain resistance genes are more effective than others in controlling multiple races of the pathogen (Balardin, R. S. et al., J. Amer. Sco. Hort. Sci. 123(6):1038-1047 (1998)).
The bean breeding line SEL 1308 derived from the highly resistant differential cultivar G2333, is known to possess the single dominant Co-42 gene for anthracnose resistance (Young, R. A. et al., Theor. Appl. Genet. 96:87-94 (1998)). When inoculated with 34 selected races of C. lindemuthianum chosen to represent a diverse sample of the pathogen population, SEL 1308 demonstrated a resistance index (RI) of 97% (Balardin, R. S. et al., J. Amer. Sco. Hort. Sci. 123(6):1038-1047 (1998)). The only cultivar with a higher RI (100%) was G2333 known to possess the combination of three independent resistance genes, Co-42, Co-5, and Co-7 (Young, R. A. et al., Theor. Appl. Genet. 96:87-94 (1998)). This three-gene combination confers resistance to all described races of the pathogen (Pastor-Corrales, M. A. et al., Plant Dis. 78:959-962 (1994)). Among the reported resistance genes, the Co-42 gene in SEL 1308 exhibits the broadest-based resistance in common bean (Balardin, R. S. et al., J. Amer. Sco. Hort. Sci. 123(6):1038-1047 (1998)).
Although plants can be bred for disease resistance traits, this can be a long and tedious process. A conventional plant breeding program requires as much as ten years to develop a new variety. Furthermore, once a new variety is introduced, it may not prove resistant to new forms of the pathogen it was selected to be resistant to. For example, new races of C. lindemuthianum pathogenic to current commercial varieties of dry bean have been identified (Balardin, R. S. et al., Plant Dis. 80:712 (1996); Kelly, J. D. et al., Plant Disease 78:892-894 (1994)). Sources of resistance to anthracnose in adapted commercial bean varieties grown in the U.S. are ineffective against these races (Kelly, J. D. et al., Plant Disease 78:892-894 (1994)), whereas new resistance sources in Mexican germplasm offers an effective solution for the control of anthracnose (Pastor-Corrales, M. A. et al., Plant Dis. 78:959-962 (1994)). For instance, resistance in the Mexican landrace variety G 2333 to 450 races of anthracnose is conditioned by a combination of three independent resistance genes (Co-42, Co-5, Co-7; Pastor-Corrales, M. A. et al., Plant Dis. 78:959-962 (1994); Young, R. A. et al., Crop Sci. 37:940-946 (1997)).
It would thus be desirable to provide disease resistant genes from legumes. No disease resistance gene has been cloned from the bean species P. vulgaris or any related legume species. It would further be desirable to provide genes associated with resistance to anthracnose. The Co-42 gene is a valuable candidate gene for molecular cloning due to its broad resistance and availability of a tightly linked marker (Young, R. A. et al., Theor. Appl. Genet. 96:87-94 (1998)). In common bean and soybean, resistance genes analogs (RGAs) have been identified using primers specific to conserved regions of known resistance genes and mapped close to known disease resistance locus (Kanazin, V. et al., PNAS (USA) 93:11746-11750 (1996); Yu, Y. G. et al., PNAS (USA) 93:11751-17756 (1996); Geffroy, V. et al., Theor. Appl. Genet. 96:494-502 (1998); Rivkin, M. I. et al., Genome 42:41-47 (1999)). Mapping of RGAs has been the only approach used to isolate known resistance gene sequences from common bean. RGAs, however, are not always closely associated with a resistance phenotype and may be loosely linked to known resistance locus limiting their value in chromosome walking to the gene. Additional approaches, such as map-based cloning are still needed to isolate resistance gene candidates in crop species. It would also be desirable to provide legume plants with disease resistance, preferably to anthracnose. It would be further desirable to transform plants using anthracnose resistant genes to produce disease resistant plants.
The present invention provides novel purified and isolated nucleic acid sequences associated with disease resistance in common bean (Phaseolus vulgaris L.). The DNA for COK-4 isolated from strain SEL 1308 is set forth in SEQ ID NO: 1 while the DNA for COK-4 isolated from P. vulgaris Black Magic is set forth in SEQ ID NO: 2. The deduced amino acid sequence of COK-4 is also provided and set forth in SEQ ID NO: 3. The predicted COK-4 protein contains a serine-threonine kinase domain with a highly hydrophobic membrane-spanning region.
Methods for making and using the DNA""s encoding for COK-4 are also provided. For example, COK-4 may be used to provide plants with disease resistance, preferably to anthracnose. Vectors containing the DNA, transgenic plants and other organisms, e.g., E. coli, transfected with said vectors, as well as seeds from said plants, are also provided by the present invention. Additional objects, advantages, and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.